Historically, tangible and humanly perceivable media was used to store information and works of authorship. More recently, computer programs and data have been stored in digital memory. Volatile memory holds data as long as power is applied. Non-volatile memory holds data after power has been removed. Current digital memory has evolved from magnetic core, to transistor-based logic. Bulk memory includes hard disks, CDs, DVDs, flash memory, and the like. Data storage capacity of digital systems continues to grow with improvements in data storage. However, even with advances in memory storage density, the amount of digital data continues to grow.
Early data storage was largely limited to computer programs and associated data. Today, books, artwork, CAD drawings, photographs, music and video are all stored digitally. New works are continuously being created, and preexisting, tangible works are scanned or otherwise digitized and stored. Improved resolution, such as higher video, picture or sound resolution requires even greater storage than prior digitization of the same work. This creates an even greater need for increased storage density, storage or retrieval speed, or cheaper storage alternatives.